The 2010 Nobel Prize illustrates the evolution of graphene from a mere curiosity to the new face of carbon. Graphene is a flat sheet of sp2 carbon atoms arranged into hexagons, giving it the appearance of a honeycomb lattice. See Geim, A. K.; Novoselov, K. S. The Rise of Graphene, Nature Materials. 2007, 6, 183-191, which may be accessed at: http://www.nature.com/nmat/journal/v6/n3/abs/nmat1849.html.
Graphite ribbons are predicted to have very interesting electronic properties which combine the relatively small band gap with high switching speeds and carrier mobility. See (A) Li, X.; Wang, X.; Li, Z.; Lee, S. Dai, H. Science 2008, 319, 1229; (B) Wu, J.; Pisula, W.; Müllen, K. Graphenes as Potential Material for Electronics, Chem. Rev. 2007, 107, 718-747, which may be accessed at http://pubs.acs.org/doi/abs/10.1021/cr068010r; and (C) Allen, M. J.; Tung, V. C.; Kaner, R. B. Honeycomb Carbon: A Review of Graphene, Chem. Rev. 2010. 110, 132-145, which may be accessed at http://pubs.acs.org/doi/abs/10.1021/cr900070d.
In order to take the full advantage of graphene as a building block in the new generation of materials, one needs to prepare it in a chemically homogeneous and well-defined state. Subtle variations in structure (zigzag vs. chair arrangement at the edges, size and shape) are known to affect the electronic properties very strongly. This challenge has to be met through the rationally designed chemical approaches to the synthesis of graphene in order to advance the future development of the field of carbon-based nanoelectronics. Not surprisingly, a number of synthetic approaches to such ribbons illustrated on the left have been developed. See Goldfinger, M. B.; Swager, T. M. J. Am. Chem. Soc. 1994, 116, 7895. Scherf, U. J. Mater. Chem. 1999, 9, 1853; and Berresheim, A. J.; Mueller, M.; Muellen, K. Chem. Rev. 1999, 99, 1747. Mallory, F. B.; Butler, K. E.; Berube, A.; Luzik, E. D.; Mallory, C. W.; Brondyke, E. J.; Hiremath, R.; Ngo, P.; Carroll, P. J. Tetrahedron 2001, 57, 3715. Several of these prior art syntheses are shown in FIG. 1.
There are both practical and conceptual limitations to the current approaches to the preparation of graphene ribbons. While the current syntheses often provide an elegant solution to the design of a symmetric functionalized graphene pieces, efficient and flexible approaches to non-symmetrically carved and/or substituted graphene substructures are, at best, scarce. See Kuninobu, Y.; Seiki, T.; Kanamaru, S.; Nishina, Y.; Takai, K. Synthesis of functionalized Pentacenes from Isobenzofurans Derived from C—H Bond Activation, Org. Lett., 2010, 12, 5287-5289, which may be accessed at: http://pubs.acs.org/doi/abs/10.1021/ol102349r.